1. Field of the Invention
The present invention relates to a part mounter and a method for mounting parts, and more particularly, to a part mounter and a method for mounting parts by which the required time and the distance equipment must move for mounting parts is minimized and the position of the parts is precisely recognized.
2. Description of the Related Art
In general, electronic parts such as semiconductor packages are mounted on a printed circuit board by using a part mounter. The part mounter picks up electronic parts supplied by a part supply portion such as a tray feeder or a tape feeder using vacuum suction and mounts the electronic parts at predetermined positions on the printed circuit board. Here, a head unit moves the electronic part to an image sensor to obtain information on the posture of the part held by a suction is nozzle. As the image sensor, a vision camera (a line CCD or an area CCD) is used. The image sensor detects state of the part held by the part suction portion so that information on the posture of the part is obtained. The part suction portion corrects the posture of the held part according to the image information and then mounts the part on the printed circuit board.
FIG. 1 is a perspective view showing the structure of a typical part mounter. Referring to the drawing, the part mounter includes a first Y-axis 12 and a second Y-axis 13, an X-axis 11 moving along the first and second Y-axes 12 and 13, and a head unit 14 installed to be capable of moving along the X-axis 11. A suction nozzle 15 is installed at the head unit 14 to be capable of rotating and moving up and down. A printed circuit board (PCB) 25 is transferred by a conveyer 19 to the position of a part 20 to be mounted. The head unit 14 moves between part feeders 18a, 18b, 18c, 18d and 18e, and the PCB 25. The suction nozzle 15 moves up and down and/or rotates to hold a part and mounts it on the PCB 25. At least one among the part feeders 18a, 18b, 18c, 18d and 18e may be a tape feeder or a tray. During a mounting process, the head unit 14 passes above an image sensor 16. The image sensor 16 is fixed at one side of the part mounter and detects the part held by the suction nozzle 15 so that it corrects a positional error generated when a part is held by the suction nozzle 15. The image sensor 16, for example, may have an image detecting device such as a vision camera (a line CCD or an area CCD).
FIG. 2 is a view schematically showing the path along which the head unit 14 shown in FIG. 1 moves. Referring to the drawing, the suction nozzle 15 of the head unit 14 picks up a part from the part feeders 18a, 18b, 18c, 18d and 18e and then moves to the position directly above the image sensor 16. The image sensor 16 senses the part held by the suction nozzle 15. Through a detecting process performed by the image sensor 16, an error generated when the part is held by the suction nozzle 15 can be recognized. Next, the head unit moves above a mounting position P on the PCB 25. The suction nozzle 15 of the head unit 14 descends and mounts the part at the mounting position P of the PCB 25. Here, to correct an error recognized through the sensing process, the head unit 14 changes its position in the coordinate system or the suction nozzle 15 rotates and then the part is mounted.
In the part mounter having the above structure, since the head unit 14 must travel from the part feeders 18a, 18b, 18c, 18d and 18e to the part mounting position P on the PCB 25 through the image sensor 16, the path of movement is long and complicated. That is, since the image sensor 16 is fixed at a particular position, the head unit 14 must move to the position directly above the image sensor 16 so as to sense the state of the held part.
FIG. 3 is a view showing an image of a state in which a part is held by the suction nozzle 15, which is taken by an image sensing apparatus. Referring to the drawing, the center of the suction nozzle 15 matches the central point A of an image 121. That is, when the suction nozzle 15 picks up a part 111 and moves just above the image sensor 16, the center of the suction nozzle 15 is designed to match the center of the image sensor 16. Thus, when a sensing process is performed by the image sensor 16, the center point A of the image 121 substantially matches the center of the suction nozzle 15. This is because a typical image recognition apparatus is fixed at one side of a part supply portion of a part mounter and the head unit 14 moves to a particular position after moving along a set path, that is, the center of the suction nozzle 15 matches the center of the image 121.
When the image sensing is performed after the suction nozzle 15 has picked up a part, the positional information of the central point O of a part is recognized with information on the size and shape of the part. Next, information on the tilt of the part is recognized by the information on the shape of the part. As shown in FIG. 3, recognizing the distance separated in the X direction and Y direction between the central point A of the image 121 and the central point O of the part 111, and a rotational degree θ is recognized and the separated distance and the rotational degree are compensated for.
However, to correct the error generated when the part is held, the image sensor 16 must be maintained in a fixed state. This is because the central point of the suction nozzle 14 must match the central point A of the monitor 121 to recognize the error when suctioning the part. Thus, if the central point of the suction nozzle 14 does not match the central point of the image 121 during the sensing process, performing correction an error is not possible. The positional information with respect to the nozzle is indirectly obtained and it is assumed that the above preconditions are met. Also, at least one of the image sensor 16 and the head unit 14 must be fixed.